Contraction Signatures Toward Dense Cores in the Perseus Molecular Cloud

Abstract

We report the results of an HCO+ (3-2) and N2D+ (3-2) molecular line survey performed toward 91 dense cores in the Perseus molecular cloud using the James Clerk Maxwell Telescope, to identify the fraction of starless and protostellar cores with systematic radial motions. We quantify the HCO+ asymmetry using a dimensionless asymmetry parameter ${\delta }_v$, and identify 20 cores with significant blue or red line asymmetries in optically-thick emission indicative of collapsing or expanding motions, respectively. We separately fit the HCO+ profiles with an analytic collapse model and determine contraction (expansion) speeds toward 22 cores. Comparing the ${\delta }_v$ and collapse model results, we find that ${\delta }_v$ is a good tracer of core contraction if the optically-thin emission is aligned with the model-derived systemic velocity. The contraction speeds range from subsonic (0.03 km/s) to supersonic (0.4 km/s), where the supersonic contraction speeds may trace global rather than local core contraction. Most cores have contraction speeds significantly less than their free-fall speeds. Only 7 of 28 starless cores have spectra well-fit by the collapse model, which more than doubles (15 of 28) for protostellar cores. Starless cores with masses greater than the Jeans mass (M/M${}_J$ > 1) are somewhat more likely to show contraction motions. We find no trend of optically-thin non-thermal line width with M/M${}_J$, suggesting that any undetected contraction motions are small and subsonic. Most starless cores in Perseus are either not in a state of collapse or expansion, or are in a very early stage of collapse.

Accepted to ApJ, 18 pages, 12 figures, 4 tables

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Cited by in corpus (13)

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• Magnetically Dominated Parallel Interstellar Filaments at the Infrared Dark Cloud G14.225-0.506
• Magnetic fields in molecular clouds: Limitations of the analysis of Zeeman observations
• Asymmetric Line Profiles in Dense Molecular Clumps Observed in MALT90: Evidence for Global Collapse
• An Ammonia Spectral Map of the L1495-B218 Filaments in the Taurus Molecular Cloud: II CCS & HC${}_7$N Chemistry and Three Modes of Star Formation in the Filaments
• Neutral vs Ion Linewidths in Barnard 5: Evidence for Penetration by MHD Waves
• A large (~1 pc) contracting envelope around the prestellar core L1544
• Alignment of dense molecular core morphology and velocity gradients with ambient magnetic fields
• Principal component analysis for estimating parameters of the L1287 dense core by fitting model spectral maps into observed ones
• Sub-structure formation in starless cores
• Prestellar Cores in Turbulent Clouds: Numerical Modeling and Evolution to Collapse
• Dense Molecular Clumps with Large Blue Asymmetries: Evidence for Collapse